Earth Orbital Parameters Research Articles

Glacial inception through rapid ice area increase driven by albedo and vegetation feedbacks

Abstract. We present transient simulations of the last glacial inception using the Earth system model CLIMBER-X with dynamic vegetation, interactive ice sheets, and visco-elastic solid Earth responses. The simulations are initialized at the middle of the Eemian interglacial (125 kiloyears before present, ka) and run until 100 ka, driven by prescribed changes in Earth's orbital parameters and greenhouse gas concentrations from ice core data. CLIMBER-X simulates a rapid increase in Northern Hemisphere ice sheet area through MIS5d, with ice sheets expanding over northern North America and Scandinavia, in broad agreement with proxy reconstructions. While most of the increase in ice sheet area occurs over a relatively short period between 119 and 117 ka, the larger part of the increase in ice volume occurs afterwards with an almost constant ice sheet extent. We show that the vegetation feedback plays a fundamental role in controlling the ice sheet expansion during the last glacial inception. In particular, with prescribed present-day vegetation the model simulates a global sea level drop of only ∼ 20 m, compared with the ∼ 35 m decrease in sea level with dynamic vegetation response. The ice sheet and carbon cycle feedbacks play only a minor role during the ice sheet expansion phase prior to ∼ 115 ka but are important in limiting the deglaciation during the following phase characterized by increasing summer insolation. The model results are sensitive to climate model biases and to the parameterization of snow albedo, while they show only a weak dependence on changes in the ice sheet model resolution and the acceleration factor used to speed up the climate component. Overall, our simulations confirm and refine previous results showing that climate–vegetation–cryosphere feedbacks play a fundamental role in the transition from interglacial to glacial states characterizing Quaternary glacial cycles.

Zanclean to gelasian high-frequency sequences of the crotone basin (southern Italy): Architectural variability and forcing mechanisms

The Zanclean Belvedere Formation and the Gelasian Strongoli Sandstone, cropping out in the Neogene to Quaternary Crotone Basin, southern Italy, exhibit a high-frequency cyclicity consisting of 10°–101 m sequences, which stack in an aggradational to progradational pattern. These high-frequency sequences are bounded by ravinement surfaces and are usually composed of transgressive and regressive deposits of similar thickness. In particular, the high-frequency sequences of the Belvedere Formation are composed of a transgressive systems tract and of a highstand systems tract, whereas those of the Strongoli Sandstone likely record also forced regression in their upper part. Due to the vertical repetition of the studied high-frequency sequences and their similar architecture despite the different tectonic settings in which the two formations accumulated, a climatic/glacio-eustatic control associated with earth-orbital parameters is very likely, as also documented in coeval successions worldwide. This contribution refines the correlation between shallow-marine sequences and their deep-water counterparts, which preserve a better record of the Milankovitch cyclicity.

Unraveling the complexities of the Last Glacial Maximum climate: the role of individual boundary conditions and forcings

Abstract. In order to quantify the relative importance of individual boundary conditions and forcings, including greenhouse gases, ice sheets, and Earth's orbital parameters, on determining Last Glacial Maximum (LGM) climate, we have performed a series of LGM experiments using a state-of-the-art climate model AWI-ESM, in which different combinations of boundary conditions and forcings have been applied following the protocol of Paleoclimate Modelling Intercomparison Project phase 4 (PMIP4). In good agreement with observational proxy records, a general colder and drier climate is simulated in our full-forced LGM experiment as compared to the present-day simulation. Our simulated results from non-full-forced sensitivity simulations reveal that both the greenhouse gases and ice sheets play a major role in defining the anomalous LGM surface temperature compared to today. Decreased greenhouse gases in LGM as compared to present day leads to a non-uniform global cooling with polar amplification effect. The presence of LGM ice sheets favors a warming over the Arctic and northern Atlantic oceans in boreal winter, as well as a cooling over regions with the presence of ice sheets. The former is induced by a strengthening in the Atlantic meridional overturning circulation (AMOC) transporting more heat to high latitudes, whilst the latter is due to the increased surface albedo and elevation of ice sheets. We find that the Northern Hemisphere monsoon precipitation is influenced by the opposing effects of LGM greenhouse gases and ice sheets. Specifically, the presence of ice sheets leads to significant drying in the Northern Hemisphere monsoon regions, while a reduction in greenhouse gases results in increased monsoon rainfall. Based on our model results, continental ice sheets exert a major control on atmospheric dynamics and the variability of El Niño–Southern Oscillation (ENSO). Moreover, our analysis also implies a nonlinearity in climate response to LGM boundary conditions and forcings.

Quantifying effects of Earth orbital parameters and greenhouse gases on mid-Holocene climate

Abstract. The mid-Holocene (MH) is the most recent typical climate period and a subject of great interest in global paleocultural research. Following the latest Paleoclimate Modeling Intercomparison Project phase 4 (PMIP4) protocol and using a fully coupled climate model, we simulated the climate during both the MH and the preindustrial (PI) periods and quantified the effects of Earth orbital parameters (ORBs) and greenhouse gases (GHGs) on climate differences, focusing on the simulated differences in the Atlantic meridional overturning circulation (AMOC) between these two periods. Compared to the PI simulation, the ORB effect in the MH simulation led to seasonal enhancement of temperature, consistent with previous findings. In the MH simulation, the ORB effect led to a markedly warmer climate in the mid–high latitudes and increased precipitation in the Northern Hemisphere, which were partially offset by the cooling effect of the lower GHGs. The AMOC in the MH simulation was about 4 % stronger than that in the PI simulation. The ORB effect led to 6 % enhancement of the AMOC in the MH simulation, which was, however, partly neutralized by the GHG effect. Transient simulation from the MH to the PI further demonstrated the opposite effects of ORBs and GHGs on the evolution of the AMOC during the past 6000 years. The simulated stronger AMOC in the MH was mainly due to the thinner sea ice in the polar oceans caused by the ORB effect, which reduced the freshwater flux export to the subpolar Atlantic and resulted in a more saline North Atlantic. This study may help us quantitatively understand the roles of different external forcing factors in Earth's climate evolution since the MH.

Remote Insolation Forcing of Orbital‐Scale South Asian Summer Monsoon Variability

AbstractWhether the South Asian summer monsoon (SASM) is controlled by local or remote insolation at the orbital band remains uncertain. Here, we perform a transient simulation forced by Earth's orbital parameters between 400 and 350 ka BP, a period characterized by significant contrast between local and remote insolation, to identify the SASM's response to insolation forcing. Simulation results suggest that the primary driver of orbital‐scale SASM variability is the Northern Hemisphere high‐latitude June insolation, as opposed to local insolation. High June insolation in the Southern Hemisphere might reduce the SASM intensity. Remote insolation influences the SASM by altering the latitudinal thermal gradient and, consequently, the meridional position of the South Asian high (SAH). The SAH is associated with intense convection and hence drives the meridional shift of the intertropical convergence zone and the SASM rain belt. Thus, orbital‐scale SASM variability is strongly related to remote insolation forcing.

Quaternary stratigraphy of southern Vietnam continental margin

This study investigates the stratigraphic architectures of the South Vietnam continental margin (SVCM) from the Pliocene to the recent period. We have utilized high-resolution seismic data and sediment core data to achieve this. The study reveals that the Quaternary sequences on the continental margin are bounded by composite erosional surfaces, which were formed due to sub-aerial erosion during periods of sea level fall and subsequent reworking processes during sea level rise. The Quaternary sequence can be divided into two subsequences: the Early Pleistocene and the Middle Pleistocene-Holocene. The Middle Pleistocene-Holocene sequences can be subdivided into six fourth-order sequences, each lasting approximately 100 to 120 thousand years. These sequences are well-preserved on the outer shelf at a modern water depth of around 100 to 120 meters. Seismic stacking patterns indicate that regressive deposits predominantly dominate the Quaternary stratigraphy of the SVCM. This means that sediment deposition during the Quaternary period was more pronounced during periods of sea-level fall. The outer shelf margin of the modern continental margin shows a south-to-southeastward migration of prograding clinoforms, indicating sediment progradation in these directions. The thick Quaternary regressive deposits preserved on the outer shelf are attributed to various factors. These factors include the low shelf gradient, tectonic subsidence, regional hinterland uplift, monsoon strengthening, and high sediment supply from the Palaeo-Mekong Delta during sea-level fall. The interaction of these factors facilitated the accumulation of thick sedimentary deposits during falling sea levels. The mid-late Pleistocene stratigraphy of the SVCM shows similarities to many other continental margins worldwide. These margins are mainly shaped under the influence of asymmetric 4th-order Milankovitch cycles. These cycles are driven by variations in Earth's orbital parameters and are characterized by longer phases of relative sea-level fall followed by shorter periods of stabilization and rise.

ENSO-like evolution of the tropical Pacific climate mean state and its potential causes since 300ka

The tropical Pacific Ocean plays a significant role in climate change, and the El Niño-Southern Oscillation (ENSO) is considered to be closely related to extreme climate phenomenon worldwide. However, the evolution of the ENSO-like patterns in the tropical Pacific during the Pleistocene glacial cycles remains controversial. In this study, we present geochemical indices and a transient model simulation to explore the ENSO-like evolution during the glacial-interglacial cycles and its driving mechanisms. Our results indicate that during the interglacial periods, the Western Pacific Warm Pool (WPWP) is characterized by the modern El Niño-like conditions with relatively decreased precipitation and weakened East Asian Summer Monsoon (EASM). By contrast, the mean state of WPWP during glacial periods is more similar to the modern La Niña-like conditions, with increased precipitation and the intensified of EASM. Spectral analyses showed that the WPWP hydrodynamics were controlled by the earth's orbital parameters through their impacts on ocean circulations. Combined with published data, we find that expansion of water masses formed in the Southern Ocean would change the deep-water redox conditions, subsurface water upwelling and surface productivity in the WPWP, and ultimately influence the ENSO-like conditions through CO2-related Walker Circulation on glacial-interglacial cycles.

Eccentricity-paced geomagnetic field and monsoon rainfall variations over the last 870 kyr

Whether there are links between geomagnetic field and Earth's orbital parameters remains unclear. Synchronous reconstructions of parallel long-term quantitative geomagnetic field and climate change records are rare. Here, we present 10Be-derived changes of both geomagnetic field and Asian monsoon (AM) rainfall over the last 870kyr from the Xifeng loess-paleosol sequence on the central Chinese Loess Plateau. The10BeGM flux (a proxy for geomagnetic field-induced 10Be production rate) reveals 13consecutive geomagnetic excursions in the Brunhes chron, which are synchronized with the global records, providing key time markers for Chinese loess-paleosol sequences. The10Be-derived rainfall exhibits distinct ~100 kyr glacial-interglacial cycles, and superimposed precessional (~23 kyr) cycles that match with those in Chinese speleothem δ18O record. We find that changes in the geomagnetic field and AM rainfall share a common ~100 kyr cyclicity, implying a likely eccentricity modulation of both the geomagnetic field and climate.

North American Midcontinent Pennsylvanian cyclothems and their implications

Abstract Cyclothems are stratigraphic sequences deposited during glacial-eustatic transgressive–regressive inundations of land. Major cyclothems are most complete on lower shelves and become separated by exposure surfaces higher on the shelf. Minor cyclothems extend only onto lower shelves or are parasequences reflecting a reversal of sea level during general phases of transgression or regression. In Midcontinent North America, highstand condensed intervals of major cyclothems are conodont-rich black shales correlated eastwards into the Illinois and Appalachian basins. The number of cyclothems decreased by loss of lesser cyclothems across these basins, signifying an eastwards increase in their depositional elevations. Generalized palaeogeographical maps show that facies successions developed across these basins during a single major interglacial transgression and regression. The control of glacial eustasy by the interaction of Earth's orbital parameters, along with radiometric dating, allows subdivision of the cyclothem succession into c. 400 kyr groupings, which reflect the longest eccentricity cycle and facilitates global correlation. Delineation of the basinward extents of regression from the disappearance of exposure surfaces elucidates the history of basin-margin development. Major cyclothems that underwent reversals of general sea-level trend display ‘splays’ of lesser cycles onto the higher shelf. Geochemical cycles ‘nested’ within deepest-water shales on low shelves appear as thin nearshore facies between exposure surfaces at their high-shelf shorelines.

The structure of marine isotope Stage 11 and its alignment with the Holocene

Marine Isotope Stage 11 (MIS 11) has long been used to estimate the natural length of the present Holocene interglacial, due to their similarity in terms of astronomically-driven insolation variations. It is debated, however, which part of MIS 11 should be aligned to the Holocene, according to different alignment strategies. Here, we use a well-dated, high-resolution Asian summer monsoon (ASM) record covering the whole of MIS 11 (from 445 to 320 thousand years ago (ky)) from stalagmite J33 from Jinfo Cave in Southwest China, to attempt to resolve the issue. The oxygen isotope (δ18O) record of stalagmite J33 enables MIS 11 to be divided into 5 stages: MIS 11a–11e. Among them, MIS 11a, MIS 11c and MIS 11e are relatively strong monsoon periods, while MIS 11b and MIS 11d are relatively weak monsoon periods. According to the similarities and differences of Earth orbital parameters between MIS 11 and MIS 1, we propose a new alignment strategy in which the interglacial maxima and their preceding glacial terminations can be aligned. This new comparison scheme shows that the “missing” parts of the Holocene correspond to MIS 11d and MIS 11e, which explains why the MIS 11 interglacial period was longer than the current Holocene interglacial.

Two-million-year record of fire in temperate East Asia

Fire is one of the most active agents in shaping terrestrial ecosystems and it has played a significant role in the complex interactions between climate, vegetation, and hominins. Here, we present records of microcharcoal and stable carbon isotopes from a two-million-year long sedimentary sequence from temperate East Asia and use it to reconstruct the long-term fire history. Our results indicate that fire frequency over the last two million years fluctuated substantially and had an inverse relationship with the abundance of C4 plants. The fire frequency during 2.1–0.3 Ma was relatively low, but after 0.3 Ma, the colder and drier climate likely resulted in much frequent fires and anthropogenic impacts probably also affected fire regime. Additionally, the charcoal time series is correlated with variations in Earth orbital parameters, suggesting the influence of orbitally-driven insolation variations on fire. During glacial periods, the dry climate contributed to increased fire activity due to the overall increase in fuel availability. A comparison of our results with global fire records confirms that insolation variations modulated by Earth orbital cycles played a key role in driving fire activity during the Quaternary.

Calendar effects on surface air temperature and precipitation based on model-ensemble equilibrium and transient simulations from PMIP4 and PACMEDY

Abstract. Numerical modeling enables a comprehensive understanding not only of the Earth's system today, but also of the past. To date, a significant amount of time and effort has been devoted to paleoclimate modeling and analysis, which involves the latest and most advanced Paleoclimate Modelling Intercomparison Project phase 4 (PMIP4). The definition of seasonality, which is influenced by slow variations in the Earth's orbital parameters, plays a key role in determining the calculated seasonal cycle of the climate. In contrast to the classical calendar used today, where the lengths of the months and seasons are fixed, the angular calendar calculates the lengths of the months and seasons according to a fixed number of degrees along the Earth's orbit. When comparing simulation results for different time intervals, it is essential to account for the angular calendar to ensure that the data for comparison are from the same position along the Earth's orbit. Most models use the classical calendar, which can lead to strong distortions of the monthly and seasonal values, especially for the climate of the past. Here, by analyzing daily outputs from multiple PMIP4 model simulations, we examine calendar effects on surface air temperature and precipitation under mid-Holocene, Last Interglacial, and pre-industrial climate conditions. We came to the following conclusions. (a) The largest cooling bias occurs in boreal autumn when the classical calendar is applied for the mid-Holocene and Last Interglacial, due to the fact that the vernal equinox is fixed on 21 March. (b) The sign of the temperature anomalies between the Last Interglacial and pre-industrial in boreal autumn can be reversed after the switch from the classical to angular calendar, particularly over the Northern Hemisphere continents. (c) Precipitation over West Africa is overestimated in boreal summer and underestimated in boreal autumn when the classical seasonal cycle is applied. (d) Finally, month-length adjusted values for surface air temperature and precipitation are very similar to the day-length adjusted values, and therefore correcting the calendar based on the monthly model results can largely reduce the artificial bias. In addition, we examine the calendar effects in three transient simulations for 6–0 ka by AWI-ESM, MPI-ESM, and IPSL-CM. We find significant discrepancies between adjusted and unadjusted temperature values over continents for both hemispheres in boreal autumn, while for other seasons the deviations are relatively small. A drying bias can be found in the summer monsoon precipitation in Africa (in the classical calendar), whereby the magnitude of bias becomes smaller over time. Overall, our study underlines the importance of the application of calendar transformation in the analysis of climate simulations. Neglecting the calendar effects could lead to a profound artificial distortion of the calculated seasonal cycle of surface air temperature and precipitation.

Orbital Influences on Conditions Favorable for Glacial Inception

AbstractGlacial cycles are driven by cyclical changes in Earth's orbital parameters: obliquity, precession, and eccentricity. A common interpretation of Milankovitch's orbital theory suggests high‐latitude June insolation is the dominant forcing in driving glacial cycles, which places emphasis on the importance of precession. However, there is abundant evidence for the importance of obliquity. Here, we use linear reconstructions based on single‐forcing climate model simulations to produce time series of climate variables important in the growth and decay of ice sheets to examine the relative influences of obliquity and precession in locations important to glacial inception. We show that obliquity can cause changes in positive degree‐days (sum of mean daily temperatures above 0°C) of larger magnitude than those of precession for Scandinavia and Baffin Island. Our positive degree‐day time series were best represented by Milankovitch's caloric summer insolation metric. Snowfall is dominated by obliquity in Scandinavia and by precession in Baffin Island.

Possible Origin of Some Periodicities Detected in Solar‐Terrestrial Studies: Earth's Orbital Movements

AbstractPeriodicities matching planetary cycles have been argued to be detected in key geophysical time series. In general, these periodicities were indirectly attributed to a planetary influence on solar activity. This supposes that planetary gravity affects the internal functioning of the Sun's dynamo, that is, the planetary hypothesis (PH) of the solar cycles. The Earth's heliocentric dynamics already includes the planetary gravitational effects on the Sun. Taking into account this fact, these periodicities, ultimately attributed to possible planetary modulations of the solar activity, could have a more direct origin in cyclical changes in the relative Sun‐Earth geometry, but then, wrongly or partially explained invoking internal solar changes. We present an original decomposition analysis of the high‐precision ephemeris DE431 from NASA/JPL in order to obtain and classify the most important planetary/lunar purely periodic changes of the Earth's orbital movement at sub‐Milanković scales. A comprehensive list of cyclic changes of the Earth's orbital parameters involved in the relative Sun‐Earth position and the Earth's speed around the Sun is given. We show that these particular geophysical quasi‐periods are identifiable in the cyclic oscillations of these orbital parameters. Since the Earth's movement in space physically affects the manner in which the solar radiant flux reaches the planet, these oscillations provide, unlike the PH, a clear, causal, and testable link for their possible attribution.

Astronomical dating of Quaternary strata in the South Yellow Sea and its indication for paleoclimatic evolution

The continental shelf has experienced high-frequency transgression-regression cycles during the Quaternary, and its sediments have stored significant information on sea-level changes, climate fluctuations and regional tectonic activities. Due to the lack of extended core records and high-resolution stratigraphic chronology, the strata correlation between continental and marine basin since the Quaternary still has considerable limitations. Here, we present a high-resolution grain size and geochemical study of core CSDP-1 (~3.5 Ma) recovered from the western South Yellow Sea (SYS), China. Two sensitive components were extracted from sediments, and their contents can be used to reflect the paleo-hydrodynamic intensity and reconstruct paleoclimate change. A comprehensive analysis including lithologic characteristics of sediments and seismic data interpretation, shows that the stratum deposition at the borehole's location is relatively continuous at the orbital time-scale. The results of spectral analysis, show that the fine sensitive component it records the periodic change information of the Earth's orbital parameters (~400-, 100-, 40-, and 20-kyr), and the astronomical chronology was established successfully. The variations of sensitive components in the sediments reveals that the SYS paleoclimate has undergone four periods since the Quaternary: cold conditions during 2.58–2.49 Ma and 1.88–0.83 Ma, warm and humid conditions during 2.49–1.88 Ma and 0.83–0 Ma. Moreover, the stratum in the SYS shelf records the Middle Pleistocene climate transition (MPT). It is inferred that the MPT in the SYS is mainly manifested by the enhancement of the 100-kyr period related to the synchronous forcing of the ~400-kyr eccentricity.

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ∼6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

South Asian Summer Monsoon precipitation variability during late Pliocene: Role of Indonesian Throughflow

Understanding the response of the South Asian Summer Monsoon (SASM) to high atmospheric pCO2 is required to predict future SASM changes under the current global warming scenario. The mid-Piacenzian Warm Period (mPWP), 3.0 to 3.3 Ma (million years ago) during the late Pliocene, provides us with such an opportunity as it had atmospheric pCO2 comparable to the present. To reconstruct SASM variability during this period, we studied multiple proxies of terrigenous input (Ti), clasticity (Ti/Ca), chemical weathering (K/Al, Mg/Al), and productivity (Ba/Al, Caexcess) in sediment collected during IODP Expedition 355 (Site U1456) spanning the mid to late Piacenzian (3.3–2.6 Ma). We find that the SASM intensified (weakened) during interglacials (glacials) of the mPWP and beyond in close correspondence with the global climate. However, we note that the SASM shifted to a higher mean state at 2.95 Ma. It could be because of the tectonically induced reorganization of the Indonesian Throughflow (ITF), which enhanced the cross-equatorial pressure gradient by changing the source of water to the southern equatorial Indian Ocean. This enhanced pressure gradient resulted in the intensification of the SASM during the late Piacenzian. During the northern hemisphere glaciation after 2.95 Ma, the SASM shows a long-term decline over and above the glacial-interglacial variability. The spectral and wavelet transform analysis indicates the control of the earth's orbital parameters, especially eccentricity, over the SASM variations during the late Piacenzian.

A 40,000 year record of vegetation, environment and climate change from Chongqing, Central China

Congping is a wetland at about 2100 m asl in Chongqing Province. It is surrounded by a shrubby grassland which grades into a mixed conifer and deciduous woodland. A record based on pollen, microcharcoal and geochemistry has been used to reconstruct an environmental history covering the last approximately 40 kyr BP. The site was wooded throughout the entire record and there were two relatively warm periods; during Marine Isotope 3 (MIS 3) and for the Holocene from about 9 kyr BP. From 27 to 18 kyr BP a gradual cooling occurred and the coldest part of the record was between 22 and 18 kyr BP when a mixed conifer cool temperate deciduous forest occurred, The warmest part of the record lasted from about 9 to 1.5 kyr BP when mixed evergreen and deciduous forest occurred. The broad pattern of changes is in accord with pollen records from Dajiuhu in Hubei, and demonstrates that this was a regional signal. A moist central China at Last Glacial Maximum (LGM) shows that the East Asian Summer Monsoon was delivering enough moisture on the mainland to sustain forest cover, even at 2120 m asl. The large-scale changes are interpreted as relating to changes in Earth's orbital parameters and sea-level changes in the South China Sea which had an impact on moisture delivery into central China. It is surmised that the westerlies which created dry climates in northeastern China trapped the summer Monsoon influence enough to keep central China moist. The Younger Dryas (YD) is present in the weathering parameters as evident in several changes in elemental abundance delivered to the sediments. The Congping record shows no clear evidence of human impact on its vegetation, and there were no local fires to have caused any vegetation changes. In the last 1.5 kyr BP a slight cooling caused a rise in conifers, a decline in broad-leaved tree taxa and increased weathering rates.

Tectonic forcing of environmental transition in Central Asia at ~11–9 Ma

A comprehensive understanding of the Neogene paleoenvironmental evolution of Central Asia is important for predicting the future climatic and environmental conditions within the region. However, our understanding of the relative roles of Tibetan Plateau (TP) uplift and global cooling in driving its paleoenvironmental evolution remain elusive. Here we present two well-dated (~16–5 Ma) independent environmental magnetic records from the northern TP, together with a comprehensive analysis of other well-dated Neogene environmental magnetic datasets for ten other sites from the northern TP. The results indicate synchronous changes in magnetic parameters which we interpret as reflecting a major environmental transition in Central Asia at ~11–9 Ma, which is supported by evidence from multiple independent paleoecological and paleoclimatic studies. A major environmental transition at 11–9 Ma is also supported by the results of linear and non-linear analyses of the magnetic records of the two studied sections. Our analyses reveal that prior to ~11 Ma, the environmental fluctuations within the QB were primarily driven by insolation variations modulated by Earth orbital parameters; however, after ~11 Ma this influence faded and there was a shift from a stable environmental system, characterized by periodic fluctuations, to an unstable system with erratic fluctuations. The timing of this phase shift in the paleoenvironment of Central Asia was not related to global cooling but it coincided with extensive tectonic activity in the TP. Together with conceptual models and previous numerical simulations results, we conclude that a major shift of the dominant driver of Central Asia paleoenvironment occurred at ~11–9 Ma and that uplift of the TP, rather than global cooling, was responsible.

Eco-environmental changes in the Chinese Loess Plateau during low-eccentricity interglacial Marine Isotope Stage 19

Eco-environmental changes during interglacials with an astronomical background similar to that of the Holocene are potentially helpful for understanding the future climatic evolution. Marine oxygen isotope stage (MIS) 19 is similar to the Holocene in astronomical background, both being characterized by a low eccentricity of the Earth’s orbit. However, MIS 19 has attracted research attention only recently and therefore less is known about eco-environmental changes during this interval, especially based on terrestrial records. In the Chinese Loess Plateau (CLP), the S7 paleosol can provide valuable terrestrial paleoclimatic and paleoenvironmental record for MIS 19. Here, high-resolution terrestrial snail records from the L8–L7 strata of the Huining, Xifeng and Luochuan sequences in the CLP were analyzed in order to characterize spatio-temporal changes in climate and eco-environment during MIS 20–18. The results show that in all three sections the late part of MIS 20 was dominated by abundant cold-aridiphilous mollusc species, indicating that cold and dry climatic conditions prevailed across the entire CLP, under the strong influence of the winter monsoon. The mollusc fauna of MIS 19 were dominated by warmth-loving and thermo-humidiphilous species that enable the definition of two climatic stages. The early part of MIS 19 (~790–778 ka) was marked by warm and humid conditions, as evidenced by high abundances of warmth-loving and thermo-humidiphilous species. This interval was slightly warmer than today and it lasted for ~12 kyr. The climate of the later part of MIS 19 (~778–761 ka) was more moderate, and increased proportions of cold-aridiphilous and warmth-loving species were recorded. The warmth of this period was similar to that of today, but the climatic fluctuations were stronger. During the early part of MIS 18 (~761–745 ka), the Xifeng and Luochuan sections in the eastern CLP still maintained high abundances of warmth-loving and thermo-humidiphilous species, indicating that the moderate climatic conditions during late MIS 19 continued during early MIS 18, lasting for another ~15 kyr, and that the influence of the summer monsoon remained strong in the eastern CLP during early MIS 18. However, in the western CLP, cold-aridiphilous species in the Huining section became dominant during early MIS 18, reflecting the prevalence of a cold and dry glacial climate, with the strong influence of the winter monsoon. These findings indicate that a steeper climatic gradient and a pronounced regional environmental difference existed between the eastern and western CLP during the early part of MIS 18. Comparison of our mollusc results with the variation of Earth orbital parameters suggested that climate changes in the CLP during MIS 20–18 were likely controlled mainly by insolation changes forced by the configuration of Earth orbital parameters. The unique orbital configuration during the low eccentricity interglacial-to-glacial transition could have strengthened the East Asian summer monsoon which favored the amelioration of the eco-environment in the CLP, especially in the eastern CLP where the summer monsoon exerted a strong influence. Thus we speculate that, under natural climatic conditions, the climate of the CLP may remain in a warm, humid state for another 30 kyr, although climatic instability and the seasonal differences between winter and summer could strengthen.